Add sugar to a saucepan with the water and heat gently, stirring until the sugar has dissolved.

Bring to the boil and bubble for 2 minutes until the mixture has become slightly syrupy in consistency.

Remove from the heat.

Add the orange and lemon juices.

Add the Limoncello.

Combine well and add to a shallow lidded container.

Once cooled, place into the freezer.

Freeze until you have a slushy consistency

Place a scoop or three of the limoncello sorbet mixture into a glass, garnish with a slice of lemon and top up with chilled Prosecco.